what code is used where you live? I've never seen that required in a non rated structure.
I know this is a bit late in the game, but you should have had wind stops nailed in between the trusses. you use 2x whatever material that leaves you with about 1 1/2" to 2" clearance from the roof deck. this allows you to slip the prop-r vent down into the eave and blocks the insulation from filling the soffit vents AND keeps any high winds from blowing the insulation all to [censored].
stuffing some batts under the prop-r vent also gets the job done, but not quite as effectively. the blow-in contractor we've used in the past would staple a diaper-lining like cloth to keep the insulation out of the eaves.
also, in the link you posted, on the same page (I think) the mf'r also sells a windstop to go under their vents. you might want to look into that.